The bug seems to be that experience orbs (XP orbs) are generating at random locations surrounding the broken block and sometimes those orbs generate inside solid blocks and sometmes the orbs fall through the world. You can hear this clearly when you are mining and lava is within earshot below the player and the orbs generate incorrectly. You'll hear the hiss of the XP orbs burning. Can probably confirm in multiplayer by having p2 watch underneath structure above which p1 is mining. Note, you do not need to be mining directly above lava, there can be several layers of solid blocks above the block being mined and it still falls through.

original report
When I mine diamonds some of the EXP is in blocks around it.
What I expected to happen: I mine the diamond and the exp comes from that.
What happened: I mined the diamond- no experience. I mine the blocks around it and get EXP

Steps to Reproduce:
1: Find diamond
2: Mine it in survival (if it helps I was using an iron pick to mine it with Unbreaking II and Efficiency 1)
3. Mine the blocks around it.